Sea cucumbers are similar to sea urchins and sea stars but are far more slender and softer. When threatened by a predator, they expel part of their internal organs as a natural defense. This is to blind and entangle the enemy so the sea cucumber has a window of escape. Some types of sea cucumbers allow predators to feed on their internal organs while they escape.Don't shed a tear for them, though, as the internal organs grow back after a while.